Solvent cleaning is generally accomplished today using a variety of highly or moderately toxic or corrosive solvents. Because of the growing concerns for personal safety and health and for the environment, federal and state governments are promulgating increasingly stringent compliance criteria for solvent manufacturers and users to ensure the health and safety of those working with and around such solvents and to ensure environmentally-sound disposal of wastes that are created. For instance, California limits the use of volatile solvents for some cleaning operations by requiring that they have a vapor pressure below about 1.0 mm Hg at 20.degree. C. For many users, because the wastes are hazardous disposal generally translates into significantly increased costs that are not reflected in the initial material cost for the solvent.
Although personal safety can be promoted Primarily by preventing direct contact and exposure to hazardous solvents or by limiting exposure below published thresholds, such precautions do not account for accidents or individual sensitivities. The flammability, volatility, cleaning ability, stability during storage, and odor are other factors that the user must also consider in choosing a particular solvent.
One solvent that has found widespread application in industrial applications is methylethylketone (MEK). Although MEK is generally considered a satisfactory solvent from a cleaning effectiveness standpoint, there is a growing concern that the toxicity and flammability of MEK exposes users to unnecessary risks. Its volatility raises environmental concerns, especially in areas where photochemical smog is a Problem. Moreover, the expense associated with the sage disposal of MEK wastes is often about 5 to 10 times the material cost for MEK, thereby making MEK an expensive solvent to use.
Increasing efforts are being devoted to developing low toxicity solvents that exhibit low flammability, low volatility, and superior cleaning ability over a wide range of debris; having a pleasant odor or are odorless; are stable during storage; and are readily disposable or recoverable. Such solvents will be safe to use not only in large scale industrial applications, but also on the much smaller scale encountered in every day household cleaning chores.
In U.S. Pat. No. 5,007,969 and U.S. patent application 07/354,529, I described solvents that preferably included a mixture of ethylene carbonate and ethylene diacetate as an important active component of the final solvent mixture. I have now discovered that better solvents can be prepared substituting ethylene dipropionate for the ethylene diacetate. Shelf life of the resulting mixture is enhanced. General utility and handling are further enhanced by substituting propylene carbonate for the ethylene carbonate.